The objective of this research is to study the response of a well-characterized tumor system (presently the R-1 sarcoma in the WAG/Rij rat) to heavy charged-particle radiation, which is available at the Berkeley Bevalac. The studies are designed to provide information on the importance of cellular processes such as repopulation, variations in cell kinetic parameters, and possible interactions of lesions produced by high- and low-LET radiation in affecting tumor response in vivo. Specifically, these studies will (1) measure the repopulation kinetics of the surviving cell population after either heavy charged-particle or X-irradiation; (2) measure post-irradiation cell kinetic parameters by flow cytometric techniques for both the entire population and the surviving population only, by using a fluorescent DNA stain of low toxicity (Hoechst 33342); cells in the various cell-cycle phases will be sorted on the basis of DNA content and used for measurements of phase-specific cell survival; (3) determine if there is a measurable interaction between unrepaired lesions produced by heavy charged-particle radiation and subsequent X-irradiation in vivo; (4) continue the development of a model of tumor response incorporating the data obtained; and (5) adapt a carcinoma cell line (the RSC-1 carcinoma growing in WAG/Rij rats) to have the in vivo to in vitro plating characteristic, and study the difference in radiation response between this tumor and the R-1 sarcoma.